A typical internal combustion engine for a motor vehicle includes multiple cylinders, their associated pistons, a crankshaft, a fuel delivery and exhaust system (including a camshaft and associated valves), and an ignition system, the combination of which makes up the primary torque generation subsystem for the vehicle. When a piston is properly engaged within a cylinder, a combustion chamber is defined by the top of the piston, the cylinder sidewalls, and a cylinder head sitting atop the cylinder. During operation of the engine, the volume of the combustion chamber is varied by moving the piston linearly within the cylinder. It is the variation in the combustion chamber volume which, ultimately, may be translated into torque for propelling the vehicle.
More specifically, in both a two-stroke and a four-stroke engine, the volume of the combustion chamber is decreased and increased, respectively, during a compression stroke and a power stroke of the piston. Prior to the compression stroke (i.e., during an intake stroke), rotation of the camshaft causes a fuel intake valve to open, which allows atomized fuel to be injected into the chamber to produce a fuel/air mixture within the chamber. During the compression stroke, the piston is pushed toward the cylinder head (or toward a “top dead center” position), which compresses the fuel/air mixture, thus increasing the mixture's thermal energy. At or near the time that the piston reaches the top dead center position, a sparkplug produces a spark within the combustion chamber. The spark ignites the compressed fuel/air mixture, causing it to combust and expand with explosive force. The force of expansion initiates the piston's power stroke, during which the exploding fuel forces the piston rapidly away from the cylinder head. During a subsequent exhaust stroke, the camshaft rotation causes an exhaust valve to open, thus allowing the gasses within the combustion chamber (e.g., the exhaust gasses) to exit the cylinder.
Each piston has a connecting rod coupled to the crankshaft, and during the power stroke, the connecting rod exerts a strong linear force on the crankshaft, which converts the linear force into a rotational force. In order to maintain the crankshaft rotation, the combustions within the multiple chambers are timed so that the linear forces exerted on the crankshaft by each piston are out of phase with each other. More specifically, a distributor of the ignition system is used to route high voltage from an ignition coil to each sparkplug in a carefully timed and correct firing order. The torque associated with the crankshaft's rotational force ultimately can be translated into axle and wheel rotation, thus enabling propulsion of the vehicle.
In practice, the above-described combustion process is not 100% efficient. For example, during each combustion cycle, a certain amount of unburned fuel remains in the combustion chamber after each power stroke, and the unburned fuel is exhausted to the atmosphere during the exhaust stroke. The quantity of fuel that remains unburned during a combustion cycle affects the vehicle's fuel efficiency. Thus, engine developers seek to improve ignition systems to increase the percentage of fuel within each chamber that is burned during each combustion cycle.
In addition, combustion of the fuel/air mixture results in the production of a variety of gasses, which are exhausted from the vehicle through the vehicle's exhaust system. For example, in a typical petroleum-fueled engine, exhaust gasses include nitrogen oxides (NOx), carbon dioxide (CO2), and carbon monoxide (CO), among other things. Some of the exhaust gasses may be harmful to humans and to the environment when they are present in sufficient quantities. Accordingly, engine developers also seek to modify fuels and ignition systems in order to reduce the quantity of potentially-harmful gasses that are exhausted into the environment.